Known underwater vehicles destined to operate at varying submersion depths have rigid hulls of substantial strength, made of materials, the specific density of which is several times greater than the specific density of water. Such hulls are heavy, therefore the buoyancy/weight ratio is small, which substantially limits payload available. Moreover, steering machinery of known underwater vehicles needed to operate a vehicle at varying submersion depth includes ballast tanks, which are pressure vessels of considerable strength, hence heavy, pumps, plumbing and auxiliaries, which makes the system heavy, complicated, and costly.
Thus there is a need for an unmanned underwater vehicle of simple and lightweight construction and substantial payload.